Add "light speed" experiment code for SafeBrowsing service.

chrome/browser/safe_browsing/database_manager.cc

Index: chrome/browser/safe_browsing/database_manager.cc
diff --git a/chrome/browser/safe_browsing/database_manager.cc b/chrome/browser/safe_browsing/database_manager.cc
index 2f89931e50aebce92e15a1c38d6b39a257741cfc..f138a3305d12e8cf3f55d2019702bc417738a343 100644
--- a/chrome/browser/safe_browsing/database_manager.cc
+++ b/chrome/browser/safe_browsing/database_manager.cc
@@ -30,6 +30,7 @@
 #include "chrome/common/chrome_switches.h"
 #include "components/metrics/metrics_service.h"
 #include "components/startup_metric_utils/startup_metric_utils.h"
+#include "components/variations/variations_associated_data.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_service.h"
 #include "url/url_constants.h"
@@ -167,6 +168,14 @@ SBThreatType GetThreatTypeFromListType(safe_browsing_util::ListType list_type) {
   }
 }
 
+// TODO(asvitkine): Experimental code for measuring start up impact of SB.
+// Remove when experimentation is complete. http://crbug.com/450037
+bool ShouldDisableSafeBrowsing() {
+  static bool disable_sb =

[gab, 2015/02/13 18:09:35]

DCHECK_CURRENTLY_ON(BrowserThread::IO);

since a static variable isn't thread-safe.

[Alexei Svitkine (slow), 2015/02/13 19:00:08]

Done.

+      !variations::GetVariationParamValue("LightSpeed", "DisableSB").empty();
+  return disable_sb;
+}
+
 }  // namespace
 
 // static
@@ -593,6 +602,10 @@ void SafeBrowsingDatabaseManager::HandleGetHashResults(
 
 void SafeBrowsingDatabaseManager::GetChunks(GetChunksCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(enabled_);
   DCHECK(!callback.is_null());
   safe_browsing_thread_->message_loop()->PostTask(FROM_HERE, base::Bind(
@@ -604,6 +617,10 @@ void SafeBrowsingDatabaseManager::AddChunks(
     scoped_ptr<ScopedVector<SBChunkData> > chunks,
     AddChunksCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(enabled_);
   DCHECK(!callback.is_null());
   safe_browsing_thread_->message_loop()->PostTask(FROM_HERE, base::Bind(
@@ -614,6 +631,10 @@ void SafeBrowsingDatabaseManager::AddChunks(
 void SafeBrowsingDatabaseManager::DeleteChunks(
     scoped_ptr<std::vector<SBChunkDelete> > chunk_deletes) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(enabled_);
   safe_browsing_thread_->message_loop()->PostTask(FROM_HERE, base::Bind(
       &SafeBrowsingDatabaseManager::DeleteDatabaseChunks, this,
@@ -622,6 +643,10 @@ void SafeBrowsingDatabaseManager::DeleteChunks(
 
 void SafeBrowsingDatabaseManager::UpdateStarted() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(enabled_);
   DCHECK(!update_in_progress_);
   update_in_progress_ = true;
@@ -650,6 +675,9 @@ void SafeBrowsingDatabaseManager::StartOnIOThread() {
   if (enabled_)
     return;
 
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(!safe_browsing_thread_.get());
   safe_browsing_thread_.reset(new base::Thread("Chrome_SafeBrowsingThread"));
   if (!safe_browsing_thread_->Start())